Fuel tank cap

ABSTRACT

A fuel tank cap structure with reduced casing body weight and improved dimensional accuracy is disclosed. The casing body of the fuel tank cap has a valve chamber, in which a positive pressure valve and a negative pressure valve are received. The casing body includes an outer tubular body and a valve chamber-forming member located inside the outer tubular body. The outer tubular body is joined with the valve chamber-forming member via a horizontal joint member and vertical horizontal members, which are arranged in a hollow portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cap of a fuel tank with a pressurecontrol valve for controlling pressure in the fuel tank.

2. Description of the Related Art

One known example of fuel tank caps is disclosed in JAPANESE UTILITYPATENT PUBLICATION GAZETTE No. 6-88606. FIG. 38 is a sectional viewillustrating a fuel tank cap 300. As shown in FIG. 38, the fuel tank cap300 includes a plastic casing body 302 screwed to a filler neck FN of afuel tank (not shown), a cover member 330 attached to the casing body302, and a negative pressure valve 340 received in a valve chamber 304of the casing body 302 for controlling pressure in the fuel tank. Thenegative pressure valve 340 includes a rubber valve body 342, a valvesupporting member 346 with a fitting aperture 346a for supporting thevalve body 342, and a spring 348 for pressing the valve body 342. Whenthe differential pressure between the tank pressure and the atmosphericpressure applied to the valve body 342 increases to or above apredetermined level, the negative pressure valve 340 opens to make thetank pressure approach atmospheric pressure.

The casing body 302 has threads 302a formed on the circumference thereofto be screwed to the filler neck FN. The casing body 302 is thusrequired to have high mechanical strength. The casing body 302 has avalve chamber 304 in which the negative pressure valve 340 is received.High dimensional accuracy is required to enhance the sealingcharacteristics of the fuel cap. If the wall thickness of the casingbody were increased to enhance the mechanical strength of the casingbody 302, then sink marks are formed in injection molding whichdeteriorate the dimensional accuracy.

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a fuel tank capwith a casing body of reduced weight and improved dimensional accuracy.

At least part of the above and the other related objects is realized bya fuel tank cap for closing an inlet of a filler neck of a fuel tank.The fuel tank cap includes: a casing body having a valve chamber andbeing molded by injecting a resin; and a pressure control valve having avalve body and being received in the valve chamber. The casing body hasa seat member, on which the valve body is seated and separated from, anda hollow portion formed at a site close to the seat member.

In the fuel tank cap of the present invention, the casing body receivesa pressure control valve in the valve chamber and has a seat member, onwhich the valve body of the pressure control valve is seated. The casingbody further includes a hollow portion formed at a site close to theseat member. The hollow portion reduces the resin contraction in thevicinity of the seat member, thereby attaining excellent dimensionalaccuracy in the seat member and ensuring high sealing characteristicsfor the seat member.

The present invention is also directed to a fuel tank cap for closing aninlet of a filler neck of a fuel tank. The fuel tank cap includes: acasing body having a valve chamber and being molded by injecting aresin; and a pressure control valve received in the valve chamber. Thecasing body includes: an outer tubular body fitted in the filler neck; avalve chamber-forming member arranged inside the outer tubular bodyacross a gap, the valve chamber-forming member defining the valvechamber; and a joint member, which joins the outer tubular body with thevalve chamber-forming member and has a hollow portion as the gap in thecasing body.

In the casing body of the fuel tank cap according to the presentinvention, the valve chamber-forming member is located inside the outertubular body across a gap. The gap between the outer tubular body andthe valve chamber-forming member forms the hollow portion. A horizontaljoint member joins the outer tubular body with the valve chamber-formingmember. In accordance with one preferable application, the horizontaljoint member is constructed as a wall surface that prevents the fueltank from being connected to the atmosphere. A plurality of verticaljoint members may be arranged in the hollow portion at predeterminedintervals in the circumferential direction to join the outer tubularbody with the valve chamber-forming member. The vertical joint memberscompensate for the lowered mechanical strength of the casing body due tothe existence of the hollow portion.

In accordance with one preferable application, the valve chamber-formingmember includes an upper cylindrical wall element having a predetermineddiameter, a lower wall element having a smaller diameter than thediameter of the upper cylindrical wall element, and a bottom elementformed on a lower portion of the lower wall element, which areintegrally formed in a cup shape to define the valve chamber. Inaccordance with another preferable application, the fuel tank capfurther includes an inner cover that closes an opening of the valvechamber-forming member. The inner cover has a positioning rib, whichextends from an outer circumference of the inner cover and is insertedin the hollow portion to position the inner cover. For example, fourpositioning ribs may be arranged at substantially identical intervalsalong the circumference of the inner cover. The inner cover may bewelded to the opening of the valve chamber-forming member by ultrasonicwelding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half sectional view illustrating a fuel tank cap embodyingthe present invention;

FIG. 2 is a half sectional view illustrating a casing body

FIG. 3 is a plan view illustrating the casing body;

FIG. 4 is a bottom view illustrating the casing body;

FIG. 5 is a half sectional view illustrating the casing body and aninner cover;

FIG. 6 is an enlarged sectional view showing an upper portion of thecasing body;

FIG. 7 is a sectional view showing the state before the inner cover iswelded to the casing body;

FIG. 8 is a perspective view illustrating the casing body;

FIG. 9 shows an operation of a ratchet mechanism;

FIG. 10 shows a process of injection molding a resilient claw element ofthe ratchet mechanism;

FIG. 11 is a sectional view illustrating a joint member for joining theupper of the casing body with the outer ring member;

FIG. 12 shows the functions of the joint member;

FIG. 13 shows one modification of the structure of FIG. 12;

FIG. 14 shows another modification of the structure of FIG. 12;

FIG. 15 illustrates a sealing structure of a gasket;

FIG. 16 is a half sectional view illustrating a cover member;

FIG. 17 is a bottom view illustrating the cover member;

FIG. 18 is a perspective view illustrating the cover member 40;

FIG. 19 shows a process of attaching the cover member to the casingbody;

FIG. 20 is a sectional view illustrating a fitting projection of thecover member;

FIG. 21 shows a process of injection molding the fitting projection ofthe cover member;

FIG. 22 is a sectional view illustrating a positive pressure valve and anegative pressure valve in the casing body;

FIG. 23 is a sectional view illustrating the positive pressure valve;

FIG. 24 shows functions of a ring groove of the positive pressure valve;

FIG. 25 illustrates functions of a seat member of the casing body;

FIG. 26 further illustrates the function of the seat member of thecasing body;

FIG. 27 shows one modification of the structure of FIG. 25;

FIG. 28 is a sectional view illustrating the negative pressure valve 70;

FIG. 29 shows functions of a tapered element 75 the negative pressurevalve;

FIG. 30 is a graph showing the relationship between the flow and thepressure of the negative pressure valve;

FIG. 31 is a plan view illustrating the cover member;

FIG. 32 is an enlarged sectional view illustrating a dischargeprojection formed on the circumference of the cover member;

FIG. 33 is a perspective view illustrating the cover member;

FIG. 34 is a graph showing the volume resistivity of the cover member atmeasuring points P1 through P4;

FIG. 35 shows the measuring points P1 through P4 of the cover member atwhich the volume resistivity of FIG. 34 is measured;

FIG. 36 is a sectional view illustrating the discharge projection in ahorizontal direction;

FIGS. 37 (A) and (B) illustrate functions of the discharge projection;and

FIG. 38 is a sectional view illustrating a conventional fuel tank cap.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a half sectional view illustrating a fuel tank cap 10embodying the present invention. The fuel tank cap 10 is screwed to afiller neck FN having an inlet FNb through which a supply of fuel is fedto a fuel tank (not shown). The fuel tank cap 10 includes a casing body20 composed of a synthetic resin material, such as, for example,polyacetal, a cover member 40 attached to an upper portion of the casingbody 20 and composed of a synthetic resin material, such as, forexample, nylon, an inner cover 50 for closing an upper opening of thecasing body 20 to define a valve chamber 23, a positive pressure valve60 and a negative pressure valve 70 received in the valve chamber 23 tofunction as pressure control valves, and a gasket GS attached to theupper circumference of the casing body 20 for sealing the casing body 20from the filler neck EN. The positive pressure valve 60 includes a valvebody 61, a valve support member 68 for supporting the valve body 61, anda means for pressing the valve body 61, such as, a coil spring 69, viathe valve support member 68. The negative pressure valve 70 includes avalve body 71, and a means for pressing the valve body 61, such as, acoil spring 78.

The positive pressure valve 60 and the negative pressure valve 70control the pressure in the fuel tank according to the followingprocess. In the state that the fuel tank cap 10 is screwed to the fillerneck FN, when the tank pressure increases and the differential pressurebetween the tank pressure and the atmospheric pressure applied to thevalve body 61 of the positive pressure valve 60 exceeds a predeterminedlevel, the valve body 61 moves upward against the pressing force of thecoil spring 69 to open the positive pressure valve 60. When the tankpressure decreases and the differential pressure between the tankpressure and the atmospheric pressure applied to the valve body 71 ofthe negative pressure valve 70 exceeds a predetermined level, on theother hand, the valve body 71 moves downward to open the negativepressure valve 70. When the positive pressure difference or the negativepressure difference between the tank pressure of the fuel tank and theatmospheric pressure becomes equal to or greater than the predeterminedlevel, the positive pressure valve 60 or the negative pressure valve 70opens to control the tank pressure to be within a predetermined rangeabout the atmospheric pressure.

The following describes the structure of the respective constituents ofthe fuel tank cap 10 of the present embodiment in detail.

FIG. 2 is a half sectional view illustrating the casing body 20, FIG. 3is a plan view of the casing body 20, and FIG. 4 is a bottom view of thecasing body 20. The casing body 20 includes an outer tubular body 21 ofa substantially cylindrical shape having threads 20a screwed to theinner wall of the filler neck FN and a valve chamber-forming member 22disposed inside the outer tubular body 21. The valve chamber-formingmember forms the valve chamber 23, in which the positive pressure valve60 and the negative pressure valve 70 shown in FIG. 1 are received.

FIG. 5 is an enlarged half sectional view illustrating the casing body20 when the inner cover 50 has not yet been set in the casing body 20.The outer tubular body 21 and the valve chamber-forming member 22 areintegrally joined with each other via a horizontal joint member 28 and aplurality of vertical joint members 29. The horizontal joint member 28is a ring element arranged slightly below the center of the valvechamber-forming member 22. The horizontal joint member 28 functions toseparate the fuel tank from the atmosphere. Hollow portions 27 areformed in the space between the outer tubular body 21 and the valvechamber-forming member 22 and defined by the horizontal joint member 28and the vertical joint members 29. The vertical joint members 29 areupright walls extending radially to join the outer tubular body 21 withthe valve chamber-forming member 22.

The valve chamber-forming member 22 includes an upper wall element 24, alower wall element 25 having a smaller diameter than the diameter of theupper wall element 24, and a bottom element 26 formed on the lowerportion of the lower wall element 25. These elements are integrallyformed to define the valve chamber 23. The valve chamber 23 has an upperchamber 23a in which the positive pressure valve 60 is received and alower chamber 23b in which the negative pressure valve 70 is received.The valve chamber-forming member 22 has an opening 24a on the upper endthereof, which is covered with the inner cover 50. A slant plane 30a isformed between the upper wall element 24 and the lower wall element 25.One end of the slant plane 30a forms a seat member 30, on which thevalve body 61 of the positive pressure valve 60 is seated.

The hollow portions 27 formed in the casing body 20 reduce the totalwall thickness of the casing body 20 and decrease the contraction ofresin in the vicinity of the seat member 30. This improves thedimensional accuracy of the seat member 30 and ensures the high sealingproperty of the seat member 30. The lowered mechanical strength of thecasing body 20 due to the existence of the hollow portions 27 iscompensated by the vertical joint members 29 which join the outertubular body 21 with the valve chamber-forming member 22. The hollowportions 27 make the casing body 20 thin, shorten the time required forcooling and curing the resin, and shorten the molding cycle.

The inner cover 50 has a central recess 52 on the center of an innercover body 51 and a cylindrical support member 53 formed along thecircumference of the central recess 52. The cylindrical support member53 is formed in a tubular shape to be inserted through the opening 24aof the valve chamber-forming member 22. The circumference of the innercover body 51 forms an outer ring element 54 having four positioningribs 57 arranged at equal intervals along the circumference. Thepositioning ribs 57 are projected downward to be inserted into thehollow portions 27 between the outer tubular body 21 and the valvechamber-forming member 22. The inner cover body 51 of the inner cover 50also has a flow aperture 58 for connecting the valve chamber 23 with theatmosphere.

The opening 24a of the valve chamber-forming member 22 is covered withthe inner cover 50, which is welded to an upper peripheral portion 24bby ultrasonic welding. FIG. 6 is an enlarged sectional view showing thestate in which the inner cover 50 is welded to the upper peripheralportion 24b, and FIG. 7 illustrates the state in which the inner cover50 has not yet been welded to the upper peripheral portion 24b.

Referring to FIGS. 6 and 7, the inner cover 50 is mounted on the upperperipheral portion 24b of the valve chamber-forming member 22. Thepositioning ribs 57 of the inner cover 50 are positioned and insertedinto the hollow portions 27, so that the cylindrical support member 53of the inner cover 50 is inserted into the upper chamber 23a. Thus, theinner cover 50 on the valve chamber-forming member 22 is positionedacross a predetermined gap Sb from the inner wall surface of the valvechamber-forming member 22. This assembly can then be exposed to anenergy source, such as, ultrasound, to fuse together the inner cover 50and the valve chamber-forming member 22 together. For example, anultrasonic horn is set on the inner cover 50 to provide ultrasonicvibrations. The ultrasonic vibration causes part of the resin to befused and welded at the joint between the upper peripheral portion 24band the inner cover 50. Part of the fused resin may flow out of thejoint. Since the narrow gap Sb is formed between the valvechamber-forming member 22 and the cylindrical support member 53 of theinner cover 50, the fused resin flows through the gap Sb to be cooledand cured. Primarily the gap Sb between the inner wall surface of thevalve chamber-forming member 22 and the cylindrical support member 53functions as a flash trap. This construction effectively prevents theresin fused caused by, for example, ultrasonic welding from entering thevalve chamber 23 or the positive pressure valve 60 and the negativepressure valve 70 and deteriorating the sealing property.

FIG. 8 is a perspective view illustrating the casing body 20. A flangemember 33 for supporting the cover member 40 (see FIG. 1) is formed onthe upper circumference of the outer tubular body 21. The flange member33 includes an inner ring member 34 formed on the outer tubular body 21,an outer ring member 35 disposed outside and slightly above the innerring member 34, and four joint members 36 arranged along thecircumference for connecting the inner ring member 34 with the outerring member 35.

The inner ring member 34 has resilient claw elements 37a formed thereon.The resilient claw elements 37a and ratchet projections 49 (see FIG. 9)of the cover member 40 constitute a ratchet mechanism 37. The ratchetmechanism 37 allows a rotation of the cover member 40 only in onedirection and, when the rotation causes a torque equal to or greaterthan a predetermined level, races the cover member 40, so as to preventthe fuel tank cap 10 from being excessively rotated in the closingdirection. FIG. 9 shows engagement of the ratchet mechanism 37. Eachresilient claw element 37a includes resilient piece 37c extending from astep element 37b on the inner ring member 34 and a click 37d formed onone end of the resilient piece 37c. The resilient piece 37c is held bythe step element 37b to overhang the inner ring member 34 across a gap37e. The ratchet projections 49 are slantly formed over the wholecircumference of a top wall 41 of the cover member 40. The ratchetprojections 49 are arranged circularly on the center portion of the topwall 41 to engage with the clicks 37d.

In the ratchet mechanism 37 thus constructed, the ratchet projection 49going toward the click 37d in a clockwise direction d1 comes intocontact with the click 37d at an obtuse angle. When the force is equalto or greater than a predetermined level at this moment, the ratchetprojection 49 presses down and rides over the click 37d. This causes thecover member 40 to be rotated relative to the casing body 20. Theratchet projection 49 going toward the click 37d in a counterclockwisedirection d2, on the other hand, comes into contact with the click 37dat an acute angle and can not ride over the click 37d. This causes thecover member 40 to be rotated integrally with the casing body 20.

The operation of the ratchet mechanism 37 is explained in the example ofopening and closing the inlet FNb with the fuel tank cap 10. When arotational force is applied in the clockwise direction dl to the covermember 40 positioned at the inlet FNb, the cover member 40 is rotatedintegrally with the casing body 20 via the ratchet mechanism 37. Theclicks 37d of the ratchet mechanism 37 engage with the ratchetprojections 49, so that the torque of the cover member 40 is transmittedto the casing body 20 and the cover member 40 is rotated integrally withthe casing body 20. The fuel tank cap 10 is accordingly screwed into theinlet FNb via the threads 20a and a one start screw (not shown). Whenthe torque exceeding a predetermined level is applied to the covermember 40, that is, when the torque applied is greater than the torquerequired for screwing the fuel tank cap 10 into the filler neck FN, theclicks 37d slide against the ratchet projections 49. This causes thecover member 40 to be raced with respect to the casing body 20 andprevents the fuel tank cap 10 from being excessively rotated in theclosing direction. When the user rotates the cover member 40 in thecounterclockwise direction d2, the cover member 40 is rotated integrallywith the casing body 20 via the ratchet mechanism 37, so that the fueltank cap 10 is removed from the inlet FNb.

As shown in FIG. 8, the inner circumference of the flange member 33forms the inner ring member 34, and the resilient claw elements 37a ofthe ratchet mechanism 37 are formed on the inner ring member 34. Thismeans that the resilient claw elements 37a are disposed on the innerside of the flange member 33. This arrangement reduces contraction ofthe resin and realizes injection molding with the high dimensionalaccuracy. Namely this arrangement reduces the dimensional errors of theresilient claw elements 37a, makes the sliding torque of the covermember 40 substantially constant, and enables the ratchet mechanism 37to work stably.

Referring to FIG. 10, the joint members 36 of the flange member 33extend outward and slightly upward from the outer circumference of theinner ring member 34. There is a space Sp between the joint members 36.The space Sp decreases the amount of the resin used for the flangemember 33 to reduce the weight, and facilitates the manufacture of theratchet mechanism 37. The position of the space Sp corresponds to thegap 37e of the resilient claw element 37a. In the process of injectionmolding the casing body 20, a slide mold SF1 is inserted through thespace Sp, so that the gap 37e of the ratchet mechanism 37 can beprovided readily.

FIG. 11 is an enlarged sectional view illustrating the joint member 36of the flange member 33. As shown in FIG. 11, the joint member 36 has anL-shaped cross section including a horizontal element 36h and a verticalelement 36v integrally formed with the horizontal element 36h. The jointmember 36 has a fragile portion that is broken to separate the covermember 40 from the casing body 20 when an excessive external force isapplied to the cover member 40, for example, due to deformation of anouter plate of the automobile (not shown). As shown in FIG. 12, Vgrooves are formed as notches 36a1 through 36a4 on the outer face of thejoint member 36, whereas V grooves are formed as notches 36b1 through36b3 on the inner face of the joint member 36. An angle (1 of the planeconnecting the notch 36a1 with the notch 36b1 is set equal to 60degrees, an angle (2 of the plane connecting the notch 36a2 with thenotch 36b2 is equal to 45 degrees, and an angle (3 of the planeconnecting the notch 36a3 with the notch 36b3 is equal to 0 degree, thatis, in the diametral direction.

These notches form the fragile portion, on which the joint member 36 isbroken and separated. When the cover member 40 receives an externalforce in a direction d3 (axial direction), a break starts from thenotches 36a1 and 36b1 to separate the joint member 36 on the planeconnecting the notches 36a1 and 36b1 with each other. When the covermember 40 receives an external force in a direction d4, a break startsfrom the notches 36a2 and 36b2 to separate the joint member 36 on theplane connecting the notches 36a2 and 36b2. When the cover member 40receives an external force in a direction d5 (diametral direction), abreak starts from the notches 36a3 and 36b3 to separate the joint member36 on the plane connecting the notches 36a3 and 36b3 with each other.

The fragile portion is readily broken when an external force is appliedto the joint member 36 of the flange member 33 in any one of thevertical direction d3, the slant direction d4, and the horizontaldirection d5. This structure eliminates a scatter of the breaking loadon the joint member 36, irrespective of the direction of the externalforce applied.

FIGS. 13 and 14 show modifications of the structure of FIG. 12 havingjoint members of different shapes with notches at different positions.Referring to FIG. 13, a joint member 136 has an L-shaped cross sectionincluding a horizontal element 136h and a vertical element 136vintegrally formed with each other. The horizontal element 136h hasnotches 136a1 and 136b1 constituting a first fragile portion, and thevertical element 136v has notches 136a2 and 136b2 constituting a secondfragile portion. The first fragile portion and the second fragileportion are broken respectively on the planes connecting thecorresponding notches to separate the joint member 136.

Referring to FIG. 14, a joint member 236 is arranged in an inclinedorientation and has notches 236a1 and 236b1 constituting a first fragileportion and notches 236a2 and 236b2 constituting a second fragileportion. Another notch 236a3 is further formed between the notches 236a1and 236a2, in order to facilitate the break of the second fragileportion. The joint member 236 may have any shape and arrangement as longas it has the first fragile portion and the second fragile portion.

FIG. 15 is an enlarged sectional view illustrating an end of the flangemember 33 of the outer tubular body 21. Referring to FIG. 15, the gasketGS is disposed below the flange member 33, and is interposed between theinlet FNb of the filler neck FN and the flange member 33. A seal supportelement 21a is formed on the lower periphery of the flange member 33.The seal support element 21a has a radius RS that is smaller than aradius RG of the outer circumferential surface of the gasket GS. Settingthe radius RS of the seal support element 21a smaller than the radius RGof the gasket GS has the following effects on the sealing property.

When the fuel tank cap 10 is screwed into the inlet FNb, the gasket GSis pressed against the seal support element 21a and sealed at twosealing lines SL1 and SL2. In the conventional structure, the sealsupport element has the same radius as that of the gasket and is sealedalong substantially the whole surface. Compared with this conventionalstructure, the structure of the embodiment has the greater sealing forceat both the sealing lines SL1 and SL2 and ensures the high sealingproperty between the fuel tank and the atmosphere.

FIG. 16 is a half sectional view illustrating the cover member 40, FIG.17 is a bottom view of the cover member 40, and FIG. 18 is a perspectiveview of the cover member 40. The cover member 40 is detachably attachedto the flange member 33. The cover member 40 includes a top wall 41, ahandle member 42 projected from the top wall 41, and a side wall 43extending from the outer circumference of the top wall 41. The covermember 40 is composed of a conductive resin and integrally formed byinjection molding. Eight fitting projections 45 are projected inside theside wall 43. The fitting projections 45 are fitted in the outer ringmember 35 of the flange member 33, so that the cover member 40 isattached to the casing body 20 via the flange member 33.

The cover member 40 is assembled to the casing body 20 in the followingmanner. As shown in FIG. 19, the opening of the cover member 40 ispositioned on the outer ring member 35 of the casing body 20, and thecover member 40 is pressed into the casing body 20. The fittingprojections 45 of the cover member 40 then come into contact with theouter ring member 35 having slits 35a. The slits 35a slightly deform theouter ring member 35 in an elastic manner when the outer ring member 35rides over the fitting projections 45. The elastic deformation of theouter ring member 35 enables the outer ring member 35 to readily rideover the fitting projections 45, so as to attach the cover member 40 tothe casing body 20. The deformation of the outer ring member 35facilitates the attachment of the cover member 40 to the casing body 20.

As shown in FIG. 19, a discharge projection 46 for discharging thestatic electricity to the filler neck FN is formed on each fittingprojection 45. When the user who is electrostatically charged manuallytouches the cover member 40 in a dried atmosphere, the staticelectricity is discharged between the discharge projections 46 of thecover member 40 and the filler neck FN. This causes the staticelectricity to be grounded to the filler neck FN and prevents the userfrom receiving a shock from the static electricity when removing thefuel tank cap 10. The discharge projection 46 is formed integrally withthe fitting projection 45. The long and narrow discharge projection 46is accordingly molded easily and reinforced by the fitting projection 45to have a sufficiently large mechanical strength. The dischargeprojections 46 have the following function when the cover member 40 isattached to the casing body 20. The discharge projections 46 arepositioned in the slits 35a of the outer ring member 35 when the covermember 40 is pressed into the casing body 20. This enables the dischargeprojections 46 to be guided by the slits 35a and further facilitates theattachment of the cover member 40 to the casing body 20.

As shown in FIGS. 19 and 20, anti-shaving projections 47 are furtherformed on the top wall 41 of the cover member 40. The anti-shavingprojections 47 are formed at the positions corresponding to the fittingprojections 45 on the side wall 43. The anti-shaving projection 47 isarranged on the approximate center of a parting line PLa and hassubstantially the same height as that of the parting line PLa. Theanti-shaving projections 47 prevent the parting line PLa from being slidagainst the outer ring member 35 of the cover member 40 and shaved. FIG.21 shows the state of injection molding the fitting projection 45 andthe peripheral elements of the cover member 40. A slide mold SF2 is usedfor injection molding since the fitting projection 45 is protruded fromthe side wall 43 and undercut in injection molding. The slide mold SF2is arranged to be slidable in the direction of the arrow in FIG. 21 andforms its trace as the parting line PLa of the top wall 41. Theanti-shaving projections 47 having substantially the same height as thatof the parting line PLa cause the outer ring member 35 to slide thereonand effectively prevent the parting line PLa from being slid against theouter ring member 35 and shaved to resin powder, when the cover member40 is rotated relative to the casing body 20 via the ratchet mechanism37.

The following describes the positive pressure valve 60 and the negativepressure valve 70 received in the valve chamber 23. FIG. 22 is anenlarged sectional view illustrating the positive pressure valve 60 andthe negative pressure valve 70. The positive pressure valve 60 isdisposed in the upper chamber 23a of the valve chamber 23, and thenegative pressure valve 70 in the lower chamber 23b. FIG. 23 is anenlarged sectional view illustrating the positive pressure valve 60.

The positive pressure valve 60 includes the valve body 61 composed of,for example, fluororubber, the valve support member 68, and the coilspring 69. The valve body 61 is a disc having a lower seat surface 62and a fitting member 65 with a valve flow hole 63 on the center thereof.The fitting member 65 has a side supporting recess 66 formed in the sidewall thereof. The valve body 61 is attached to the valve support member68 by fitting the fitting member 65 into a fitting aperture 68a of thevalve support member 68. A spring support element 68b is formed on theupper surface of the valve support member 68. The spring support element68b supports one end of the coil spring 69, whereas the other end of thecoil spring 69 is supported by the cylindrical support member 53 of theinner cover 50 (FIG. 22). Namely the coil spring 69 is held between theinner cover 50 and the valve support member 68.

The positive pressure valve 60 thus constructed controls the pressure inthe fuel tank in the following manner. In the state that the fuel tankcap 10 is attached to the filler neck FN, when the tank pressureincreases to exceed a predetermined level, the valve body 61 and thevalve support member 68 lift up against the pressing force of the coilspring 69, and the fuel tank is connected to the atmosphere via thevalve chamber 23. When the connection returns the pressure in the fueltank to or below the predetermined level, the valve body 61 is presseddown by the pressing force of the coil spring 69 and closed. The valvebody 61 opens and closes in this manner, to make the differentialpressure applied thereto not greater than the predetermined level.

A rear face 62a of the valve body 61 is supported by the lower face ofthe valve support member 68. A ring recess 64 is formed in the outercircumferential portion of the valve body 61. A ring groove 61b isformed in the seat surface 62 of the valve body 61 and located insidethe ring recess 64.

The ring recess 64 and the ring groove 61b have the following functionsand effects. When the valve body 61 of the positive pressure valve 60 ismoved from the open position in the closing direction by the pressingforce of the coil spring 69 as shown in FIG. 24, the seat surface 62 ofthe valve body 61 comes into contact with the seat member 30. The seatmember 30 is thus in contact with the center of the seat surface 62having the ring recess 64. Since the valve body 61 has a thin wall atthe ring recess 64, the seat surface 62 is deformed by the seat member30.

When the seat surface 62 is pressed against the seat member 30, thevalve body 61 is seated onto the seat member 30 while keeping thehorizontal attitude and being supported by the valve support member 68on both the inner circumferential side and the outer circumferentialside of the ring recess 64. The seat surface 62 is in line contact withthe ridge of the seat member 30 and is seated not in the inclinedattitude but in the horizontal attitude, thereby ensuring high sealingproperty. The small contact area between the seat surface 62 and theseat member 30 realizes the ideal valve-opening characteristic, that is,an abrupt rise in the open position. The ring groove 61b is formed inthe seat surface 62 of the valve body 61 to equalize the deflection inthe vicinity of the ring recess 64 of the seat surface 62, therebyfurther improving the sealing property.

The seat member 30 of the casing body 20 has the shape discussed below.As shown in FIG. 25, the seat member 30 is formed on the apex of anacute angle with respect to the seat surface 62 of the valve body 61.This structure enables a line contact in the sealed position andimproves the sealing property. An angle (1 of the slant plane 30a of theseat member 30 is set equal to 25 degrees, in order to exert thefollowing effects.

A radius r1 of the seat member 30 is a critical design feature requiredto achieve the high sealing property of the present invention. When theseat member 30 has the radius r1, the comparison of the case where theangle θ1=25 degrees with the case where the angle θ1=45 degrees as shownin FIG. 26. Because of the limit of resin molding, there issubstantially no difference in a radius r2 between these two cases. Theseat member 30 accordingly has a wall thickness VT1 in the case of theangle θ1=25 degrees and a wall thickness VT2 in the case of the angleθ1=45 degrees, where VT1 is less than VT2. The smaller angle θ1 of theseat member 30 reduces its wall thickness VT1 and decreases the sinkmark due to the resin contraction. This increases the plane accuracy ofthe seat member 30 and improves the sealing property.

FIG. 27 is a sectional view illustrating a modified structure of theseat member 30 shown in FIG. 25. In the structure of FIG. 27, a seatmember 130 has a first slant plane 130a and a second slant plane 130bformed on either side thereof. The first slant plane 130a has an angleθ1=25 degrees and the second slant plane 130b has an angle θ3=45degrees; that is, the angle between the two slant planes is 110 degrees.When the radii r1 and r2 of the seat member 130 are fixed to givenvalues, the greater angle of the second slant plane 130b reduces a wallthickness VT3 and further improves the plane accuracy of the seat member130.

FIG. 28 is a sectional view illustrating the negative pressure valve 70,and FIG. 29 is an enlarged sectional view illustrating an essential partof the negative pressure valve 70. The negative pressure valve 70includes the valve body 71 composed of a resin, and the coil spring 78spanned between a spring support step 72 of the valve body 71 and thebottom element 26 for pressing the valve body 71. A seat member 76extends upward from the valve body 71 to be seated on and separated fromthe valve body 61 of the positive pressure valve 60.

The negative pressure valve 70 works in the following manner. When thefuel tank has the negative pressure relative to the atmospheric pressureand the differential pressure applied to the valve body 71 becomes equalto or greater than a predetermined level, the valve body 71 movesdownward against the pressing force of the coil spring 78 as shown inFIG. 29. The valve body 71 is accordingly separated from the seatsurface 62 of the valve body 61. At this moment, the valve body 61 isseated on the seat member 30. In that state, a passage is made betweenthe valve body 71 and the valve body 61. The fuel tank is thus connectedto the atmosphere via the passage between the valve body 71 and thelower wall element 25 and a connection aperture 26a of the bottomelement 26. This cancels the state of negative pressure in the fueltank. When the differential pressure applied to the valve body 71 isless than the pressing force of the coil spring 78, the valve body 71 isclosed.

As shown in FIG. 29, the valve body 71 of the negative pressure valve 70has a tapered element 75 on an outer circumferential member 74. Thetapered element 75 is tapered to make the distance from the lower wallelement 25 of the valve chamber-forming member 22 gradually narrower.The tapered arrangement enables the negative pressure valve 70 to havethe flow property shown in FIG. 30. FIG. 30 shows the relationshipbetween the differential pressure and the flow Q, where the solid lineshows data of the negative pressure valve 70 of the embodiment and thebroken line shows data of a comparative example corresponding to a knownpressure valve.

It is preferable that the negative pressure valve 70 has the property ofabruptly increasing the flow Q as shown by the one-dot chain line, inorder to keep the pressure in the fuel tank within a predeterminedrange. Whereas the flow Q gradually increases with an increase indifferential pressure in the comparative example, the flow Q abruptlyincreases in the negative pressure valve 70 of the embodiment, which isclose to the ideal flow property. The tapered arrangement of the taperedelement 75 of the negative pressure valve 70 increases the differentialpressure applied to the valve body 71 and thereby abruptly increases thevalve-opening force.

Referring back to FIG. 28, the connection aperture 26a is formed in thebottom element 26 of the casing body 20. The connection aperture 26a isarranged apart from the sealed portion of the valve body 71, that is,close to the center of the bottom element 26. Even when the fuelcontaminated with foreign matters flows through the connection aperture26a into the lower chamber 23b, the position of the connection aperture26a enables the fuel to hit against the valve body 71 and be returned tothe fuel tank through the connection aperture 26a. This prevents foreignmatter present in the fuel from entering the sealed portion of the valvebody 71. The foreign matters accordingly do not interfere with theopening and closing operations of the valve body 71 nor damage thesealing property.

FIG. 31 is a plan view illustrating the cover member 40, and FIG. 32 isan enlarged sectional view showing the lower end portion of the covermember 40. As shown in FIGS. 31, 32, 16, and 17, the four dischargeprojections 46 for discharging the static electricity to the filler neckFN are formed on the inner surface of the side wall 43 of the covermember 40 to be arranged at the interval of 90 degrees along thecircumference. When the user who is electrostatically charged manuallytouches the cover member 40 in a dried atmosphere, the staticelectricity is discharged between the discharge projections and thefiller neck FN and grounded to the filler neck FN.

The conditions of electric discharge whereby the user is not shockedwhen removing the fuel tank cap 10 are: (1) that discharge ofelectricity is securely performed irrespective of the closing state ofthe fuel tank cap 10; and (2) that discharge of electricity proceedsgently and does not cause a large shock. The discharge projections 46have the following structure in order to satisfy these conditions.

(1) As shown in FIG. 32, the discharge projections 46 are projected inthe axial direction, and a discharge distance L1 from the filler neck FNis set to be not greater than about 1 mm or preferably not greater thanabout 0.85 mm. When the discharge distance L1 is greater than about 1 mmthe break voltage increases and the gentle discharge characteristics arenot obtained.

(2) The discharge projections 46 are formed as long and narrowprojections in an opening-closing direction d3 of the fuel tank cap 10,that is, in the axial direction. In response to the opening or closingoperation of the fuel tank cap 10, the cover member 40 moves integrallywith the casing body 20 relative to the filler neck FN in theopening-closing direction d3. The discharge projections 46 also move inthe same direction, and the discharge distance L1 from the end of theinlet FNb of the filler neck FN is constant in the range of a length L2in the axial direction. Namely the discharge distance L1 is allowed tobe constant in the range of the length L2 irrespective of the closingstate of the fuel tank cap 10. This ensures the stable dischargecharacteristics.

(3) As shown in FIG. 31, the discharge projections 46 are arranged atthe angle of 45 degrees with respect to the handle member 42 of thecover member 40. This arrangement is ascribed to the following reason.As shown in FIGS. 31 and 33, the handle member 42 of the cover member 40is projected from the top wall 41 and injection molded to have themaximum resin contraction in a radial direction D1 and the minimum resincontraction in another radial direction D2, which is perpendicular tothe radial direction D1. If the discharge projections 46 are arranged inthe radial directions D1 and D2, the discharge distance from the fillerneck FN is varied to change the discharge characteristics. The dischargeprojections 46 are accordingly arranged in radial directions D3 and D4of 45 degrees, which give the intermediate resin contraction betweenthose in the radial directions D1 and D2. Namely the four dischargeprojections 46 are arranged concentrically with the center of the covermember 40. Irrespective of the closing state of the fuel tank cap 10,the four discharge projections 46 are arranged on the same circle aboutthe center of the cover member 40. This makes the discharge distancefrom the end of the filler neck FN constant and ensures stable dischargecharacteristics.

(4) As shown in FIGS. 16, 31, and 33, discharge slits 46a havingsubstantially the same length as that of the discharge projection 46 areformed on both sides of each discharge projection 46. The dischargeslits 46a separate the forces in the directions of arrows b1 and b2accompanied by the resin contraction in the first and the second radialdirections D1 and D2, thereby reducing the effect of resin contractionon the discharge projection 46 and decreasing the variation in dischargedistance L1.

(5) The volume resistivity of the cover member 40 is about 10⁴ to about10⁹ Ωcm. The volume resistivity at the site of the discharge projections46 is lower than the other portions of the cover member 40. The upperlimit of the volume resistivity is set to be not greater than about 10⁹Ωcm to ensure the electrical conductivity, whereas the lower limit isset to be not less than about 10⁴ Ωcm to prevent the voltage between thedischarge projection 46 and the filler neck FN from increasing abruptly.The lower volume resistivity at the site of the discharge projections 46enables the static electricity in the cover member 40 to be quickly ledto the discharge projections 46. The discharge projections 46 enable thestatic electricity in the cover member 40 to be gently discharged andgrounded via the filler neck FN, without causing an abrupt increase involtage between the discharge projections 46 and the filler neck FN.

The volume resistivity of the cover member 40 discussed above isobtained by mixing conductive whiskers, conductive fillers, orconductive carbon with the resin material for injection molding. FIG. 34is a graph showing the volume resistivity at various measurement pointson the cover member 40. FIG. 35 shows measurement points P1 through P4on the cover member 40. In the graph of FIG. 34, a measurement curve Adenotes the volume resistivity when 5 parts by weight of conductivewhiskers and 10 parts by weight of conductive carbon are mixed with 100parts by weight of polyamide (PA). A measurement curve B denotes thevolume resistivity when 20 parts by weight of conductive carbon aremixed with 100 parts by weight of polyamide (PA). One example of theconductive whiskers is Dentol (trade name, manufactured by OtsukaChemical Co., Ltd.), and one example of the conductive carbon is BalkanXC-72 (trade name, manufactured by Cabot Co., Ltd.)

The conductive material, such as conductive whiskers, conductivefillers, or conductive carbon, is mixed with an insulating resinmaterial, such as polyamide. Using only a conductive resin to obtain theabove volume resistance lowers the resulting mechanical strength of thecover member 40 and does not fulfill the anti-shock condition of thecover member 40.

The measurement points P1 through P4 of the cover member 40 shown inFIG. 35 are set to have the volume resistivity shown in FIG. 34. Thevolume resistivity at the measurement point P4 on the dischargeprojection 46 is set to be lower than those at the measurement points P1through P3 on the cover member 40. This is attained by the followingprocess. A gate Gt of an injection molding machine is set on the centerof the cover member 40 as shown in FIG. 35. The molten resin is chargedfrom the gate Gt through the top wall 41 and the side wall 43 to thedischarge projections 46. The conductive material is collected at ahigher density at positions further from the gate Gt. The dischargeprojections 46 are set at the final charging position of the moltenresin that is injected from the gate Gt. This causes the conductivematerial to be collected at a higher concentration in the dischargeprojections 46 than in any other part of the cover member 40, therebyenhancing the electrical conductivity of the discharge projections 46.

As discussed previously, the discharge slits 46a are formed on bothsides of each discharge projection 46 along the circumference. Thedischarge slits 46a surround the discharge projection 46 and lead theflow of molten resin to the final charging position, thereby furtherincreasing the density of the conductive material and improving theelectrical conductivity.

(6) FIG. 36 is a sectional view of the discharge projection 46 in thehorizontal direction. As shown in FIG. 36, the discharge projection 46has a semi-circular-shaped top portion 46b. A planar top portion 46Ab ofa discharge projection 46A shown in FIG. 37(A) often causes an abruptdischarge of electricity, whereas a sharp top portion 46Bb of adischarge projection 46B shown in FIG. 37(B) causes a gentle dischargeof electricity. For better discharge characteristics, it is thuspreferable that the discharge projection has the sharp top portion likethe discharge projection 46B. The sharp top portion 46Bb of thedischarge projection 46B, however, causes a recess of a mold for moldingthe discharge projection 46B to be clogged and makes it difficult toremove the resin residue. In this embodiment, the discharge projection46 accordingly has a semi-circular-shaped top portion 46b, whicheffectively allows the resin residue to be removed from the mold andforms the discharge projection 46 to the fixed shape.

The present invention is not restricted to the above embodiment, butthere may be many other modifications, changes, and alterations withoutdeparting from the scope or spirit of the main characteristics of thepresent invention.

(1) In the above embodiment, the discharge projections 46 are formedintegrally with the cover member 40. As long as the dischargeprojections 46 have the function of sufficiently dischargingelectricity, they may be formed separately from the cover member.

(2) In the embodiment, the discharge projections 46 are formed by theinjection molding to have the smaller volume resistivity than any otherpart of the cover member 40. Another possible process applies aconductive material on the surface of the discharge projections 46.

(3) In the above embodiment, the electricity is discharged between thedischarge projections 46 and the filler neck FN. The discharge ofelectricity may, however, be carried out between the dischargeprojections 46 and a member of the automobile body as long as it facesthe discharge projections 46 and can ground the static electricity inthe cover member 40.

It should be clearly understood that the above embodiment is onlyillustrative and not restrictive in any sense. The scope and spirit ofthe present invention are limited only by the terms of the appendedclaims.

What is claimed is:
 1. A fuel tank cap which closes an inlet of a fillerneck of fuel tank, said fuel tank cap comprising:a casing body,fabricated by resin injection molding, having a valve chamber, saidcasing body being molded by injecting a resin; and a pressure controlvalve received in said valve chamber, said casing body comprising: anouter tubular body arranged to be fitted in said filler neck, an upperpart of said outer tubular bodv supporting a casket attached to saidfiller neck; a valve chamber-forming member located inside said outertubular body across a gap, said valve chamber-forming member definingsaid valve chamber; and a horizontal ioint member of a disk shape formedbetween said outer tubular body and said valve chamber-forming member,said horizontal joint member separating the gap into an upper hollowportion and a lower hollow portion and being located at a position lowerthan said gasket.
 2. A fuel tank cap in accordance with claim 1, whereinsaid valve chamber-forming member comprises an upper cylindrical wallelement, a lower wall element smaller than said upper cylindrical wallelement, and a bottom element formed on a lower portion of said lowerwall element, said upper cylindrical wall element, lower wall elementand bottom element being integrally formed in a cup shape to form saidvalve chamber.
 3. A fuel tank cap in accordance with claim 2, whereinsaid joint member comprises vertical joint members extending verticallybetween said valve chamber-forming member and said outer tubular body ina radial direction, said vertical joint members being arranged in saidgap to connect said outer tubular body with said valve chamber-formingmember.
 4. A fuel tank cap in accordance with claim 2, wherein a seatmember is located below said valve chamber-forming member and close tosaid horizontal joint member.
 5. A fuel tank cap in accordance withclaim 4, wherein said seat member comprises an inclined plane forjoining said upper cylindrical wall element with said lower wall elementalong the circumference of said upper cylindrical wall element.
 6. Afuel tank cap in accordance with claim 1, said fuel tank cap furthercomprising:an inner cover that closes an opening of said valvechamber-forming member, wherein said inner cover has positioning ribsextending from an outer circumference thereof, said positioning ribsbeing inserted in said hollow portion to position said inner cover.
 7. Afuel tank cap in accordance with claim 6, wherein said positioning ribsare arranged at 90-degree intervals along the circumference of saidinner cover.
 8. A fuel tank cap in accordance with claim 7, wherein saidinner cover has been welded to the upper portion of valvechamber-forming member by ultrasonic welding, so that said opening iscovered by said inner cover.
 9. A fuel tank cap in accordance with claim8, wherein said inner cover comprises a cylindrical support member thatis inserted through said opening, said cylindrical support member beinginserted within said upper cylindrical wall element of said valvechamber-forming member across a predetermined gap.